This invention relates to an electrical generating power plant including a Compressed Air Energy Storate (CAES) system. More particularly this invention relates to a CAES system which stores excess power from an electrical power generating plant during off-peak hours, and returns the stored energy as peak power when required. More particularly, this invention relates to a CAES system which is fueled with low BTU coal gas generated in a continuously operating pressurized air coal gasifier, the coal gas being stored in a coal gas reservoir during off-peak hours.
The electric utility industry has as its main objective the supply of power at the lowest possible cost. This purpose has led to the development of large sophisticated nuclear and fossil-fuel-fired steam generating plants. For both technical and economical reasons, these plants should be operated at a steady load. However, to meet daily and seasonal fluctuations in power demand, the industry uses so called peaker units. The most common form of these units are gas turbine systems that use premium fuels such as natural gas and oil.
Because of the limited supply of oil and natural gas in this country and current problems in the supply of petroleum fuel from foreign sources, premium fuel has become very expensive and the long-term supply is uncertain. Therefore, electric utilities have been exploring better ways of utilizing, or even eliminating, the use of premium fuels for peaker units and the possibility of operating their large power plants at steady or constant load. These considerations have led to the investigation of energy storage systems.
Studies conducted by electric utilities indicate that CAES power plants are attractive for consideration as an energy storage system. A CAES plant may comprise a gas turbine-generator set, a combustor to preheat the air, a compressor system, and an underground air storage reservoir. In contrast to conventional peaker units, the turbine system and compressor system are uncoupled; each system operates independently.
The purpose of this arrangement is twofold. Firstly, the compressor system is driven with cheap off-peak power from the main power generating plant and the energy is stored as compressed gas in a compressed gas reservoir. Secondly, during peak hours the compressed air stored in the reservoir is utilized to run the turbines at their full power. This is in contrast to a conventional gas turbine peaker unit wherein the total power output is reduced by one or two thirds. The reason for this reduction in power is because that portion of the system's power is used internally to operate compressors which are needed to supply compressed air to the turbine. By utilizing a CAES system fuel savings on the order of 50% to 60% are possible. However, the CAES systems still have the problem of not completely eliminating the need for premium fuel.
It is an object of the present invention to provide an improved CAES power plant which substantially eliminates the need for premium fuel. This invention utilizes a unique combination of a CAES system, a high pressure continuously operating coal gasifier, and a coal gas storage reservoir.